"In 1911 superconductivity was first observed in mercury by Dutch physicist Heike Kamerlingh Onnes of Leiden University (shown above). When he cooled it to the temperature of liquid helium, 4 degrees Kelvin, its resistance suddenly disappeared."

Superconductors are materials that have no electrical resistance and conducts
electricity with zero energy loss. This class of materials is diamagnetic, meaning
that it will levitate permanent magnets. These bizarre properties make superconductors
a unique and interesting material to research and to use in future applications.
Unfortunately, superconductors experience these bizarre properties only under
the influence of a very low temperature environment (requires liquid helium, liquid
hydrogen, liquid nitrogen or liquid oxygen).

Theoretically, any substance can be a superconductor when frozen to an appropriate
temperature. Scientists attempt to discover "high temperature"superconductors
by methods of trial and error. The first element that was discovered to have superconductive
properties at 4 K was mercury, which was discovered in 1911 by Heike Kamerlingh
Onnes. The element that has the highest superconducting critical temperature of
9.3 K was niobium. The highest critical temperature for an ordinary compound
is Nb3Ge, which has a critical temperature of 23 K. In 1986, a
superconducting ceramic [(LaBa)3CuO4] was discovered to
be superconductive at 30 K by Johann Georg Bednorz, Karl Alex Müller.

Currently, the superconductor with the highest critical temperature ever recorded
is Mercury Barium Thallium Copper Oxide or Hg0.2Tl0.8Ca2Cu3O,
which has a critical temperature of 139 K at one atmosphere. This superconductor
is a type of ceramic copper oxide and its critical temperature was determined
in 1995 by Chakoumakos, Dai, Wong, Sun, Lu, and Xin. Apparently, metal-copper
oxide ceramic superconductors have high critical temperatures, which might unlock
the key of synthesizing a high temperature superconductor that is superconductive
under room temperature conditions.